Unit rate for travel 250 mild in 5 hours

250 miles in 5 hours can also be written as 250/5 and since you are looking for a unit rate we must make the denominator 1 so we can divide both sides by 5 and get 50/1 in other words the unit rate is 
50 miles per hour

The unit rate is 50 because you have to divide to get the unit rate